The clinical investigation of patients with destructive periodontal disease is part of a unified study of the interactions between host and microbial factors which underlie the disease process. Longitudinal changes in untreated patients will be monitored by clinical indices, attachment level measurements, and radiographic techniques. The rate and localization of destruction in individual sites will be assessed and compared with changes in the clinical parameters. These changes will be evaluated in relationship to alterations of the microbial flora and changes in the host response. The effect of therapeutic procedures including mechanical debridement and antiseptic or antibiotic agents on clinical parameters of disease and microbial populations will be assessed. As part of the evaluation procedure, the reproducibility of a spectrum of clinical measurements will be determined as well as their relationship to destruction of bone or the attachment apparatus. In order to extend diagnostic capabilities, more sensitive methods of clinical measurement and laboratory techniques for diagnosis of disease will be evaluated. Results of longitudinal studies of untreated patients demonstrated that destruction does not take place at equal rates in all periodontal lesions, but is highly localized. Attachment loss at rates of greater that 2 mm in 2 months have been detected in individual sites. Replicate attachment level measurements at two-month intervals and repeated standardized radiographs appear to be sensitive indicators of "active" disease.